Manifold pressure, fuel pressure, brake pressure, refrigerant pressure and boost pressure are commonly measured with semiconductor pressure sensors. A tiny diaphragm deflects under pressure, and integrated electronics convert that deflection into a usable signal.
A pressure sensor can fail electrically, but the system can also produce a genuinely abnormal pressure. This distinction is central to diagnosis. A low fuel-rail pressure reading may be caused by a weak pump, leaking injector, restricted supply, faulty regulator or bad sensor. The scan-tool number is evidence, not a verdict.
Pressure plausibility can often be checked against another reference. MAP with key on and engine off should usually be close to barometric pressure. A/C pressure should change with system operation and temperature rather than remain frozen. Brake pressure should respond to pedal application. Fuel pressure should respond in a way consistent with commanded pump and engine load.
When possible, compare the electronic reading with a trusted mechanical gauge or known reference condition. If the scan value and physical measurement disagree significantly, then investigate the sensor and its circuit. If they agree, the sensor may be reporting a real system problem.